The present invention relates to the field of optical shutters and, particularly, pertains to optical shutters which operate in the near-infrared and/or visible wavelength regions. More specifically, this invention pertains to optical shutters comprising one or more photon absorbing materials, such as an organic free radical compound that converts absorbed photons to heat in less than 1 nanosecond, and one or more reversible thermochromic polydiacetylene materials.
Throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent specifications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
As the quantity and speed of data communications over fiber optics systems rapidly increases due to the growing demand from Internet usage and other communications, all-optical switching systems are of increased interest to overcome the high cost and slow switching speeds of conventional switches. These conventional switches include, for example, various mechanical switches, electro-optic switches, and thermo-optic switches, such as, for example, described in U.S. Pat. Nos. 5,732,168 and 5,828,799, both to Donald. In particular, the increased complexity and cost of switching systems which involve switching from an optical signal to an electrical signal and then back to an optical signal have increased the level of interest in all-optical switches.
An all-optical switch typically switches an optical signal from one output port to another. This is typically accomplished by applying an input pump signal from a pump laser source to cause the optical signal to be selectively switched. The switch is responsive to the laser pump signal to selectively switch the light of the optical signal to one or the other of the output ports.
A variety of approaches are known for making all-optical or hybrid optical switches, such as, for example, described in U.S. Pat. No. 5,905,587 to Maeno et al.; U.S. Pat. No. 5,923,798 to Aksyuk et al.; U.S. Pat. No. 5,970,185 to Baker et al.; U.S. Pat. No. 5,841,912 to Mueller-Fiedler et al.; U.S. Pat. No. 5,757,525 to Rao et al.; U.S. Pat. No. 5,872,648 to Sanchez et al.; U.S. Pat. No. 5,091,984 to Kobayashi et al.; U.S. Pat. No. 5,406,407 to Wolff; U.S. Pat. No. 5,740,287 to Scalora et al.; U.S. Pat. No. 5,960,133 to Tomlinson; and U.S. Pat. No. 5,539,100 to Waslielewski et al. For example, as described in U.S. Pat. No. 5,943,453 to Hodgson; one basic configuration for an all-optical switch is a Mach-Zehnder interferometer which includes a first fiber optic input arm for receiving an input optical signal and a second fiber optic input arm for receiving a switching pump signal. The input arms are fused together to form a first coupler which subsequently branches out into two intermediate arms. The first coupler splits the input light signal into equal portions which then enter the two intermediate arms. The two intermediate arms are once again fused to form a second coupler which branches into two output arms. After traveling through the two intermediate arms, the two signals are recombined by the second coupler. If the two signals are in phase at the second coupler, then all the light is coupled into a first one of the two output ports. If the two signals are completely out of phase, then the light is coupled into the other of the two output ports. The reliability of the Mach-Zehnder interferometer for optical switching is typically sensitive to temperature-dependent effects.
The need for improved optical switches is increased by the use of wavelength add/drop multiplexing (WADM) which converts the optical signal in the optical fiber into, for example, 16 signals at 16 different wavelengths in a near-infrared range of about 1540 to 1560 nm, as, for example, described in Bell Labs Technical Journal, January-March 1999, pages 207 to 229, and references therein, by Giles et al.; and in U.S. Pat. No. 5,959,749 to Danagher et al. There is about 1 nm between the wavelength channels. The primary function of the optical switch is to add and/or drop optical signals from the multiple wavelengths traveling through the optical fiber. It would be highly desirable to have arrays of optical switches to handle the optical signals from multiple wavelengths per optical fiber and multiple optical fibers, such as up to 100xc3x97100 or greater optical switch arrays. Also, it would be highly desirable if the response time for the optical switch is ultrafast, such as 1 nanosecond or less.
It would be advantageous if an all-optical switching system were available which avoided the complexity and cost of hybrid electro-optic and other systems while increasing the speed of the switching times from the millisecond range to the nanosecond or picosecond ranges.
One aspect of the present invention pertains to an optical shutter comprising (1) an organic free radical compound in which the free radical compound is photon-absorbing and (2) a polydiacetylene compound, wherein the polydiacetylene compound is characterized by having a change in absorption in a wavelength region as a result of a photo-induced heat transfer from the free radical compound. In one embodiment, the free radical compound is a radical cation, preferably an aminium radical cation. In one embodiment, the free radical compound is a radical anion, preferably an anthrasemiquinone radical anion.
In one embodiment of the optical shutter of this invention, the change in absorption is reversed by cooling to a temperature of less than 50xc2x0 C. In one embodiment, the change in absorption is reversed by cooling to a temperature of less than 75xc2x0 C. In one embodiment, the change in absorption is reversed by cooling to a temperature of less than 110xc2x0 C.
In one embodiment of the optical shutter of this invention, the change in absorption as a result of the photo-induced heat transfer is reversed by a photo-induced reaction. In one embodiment, the optical shutter comprises a photosensitizer compound and the photo-induced reaction is sensitized by the photosensitizer compound. In one embodiment, the photo-induced reaction is a photo-induced reversible electron transfer reaction.
In one embodiment of the optical shutter of the present invention, the optical shutter is utilized in an optical switch for a fiber optics communications channel. In one embodiment, the optical shutter is utilized in a viewing lens of an eyewear device. In one embodiment, the optical shutter is utilized in a laser protection device for protection of eyes or sensors from a source of laser radiation. In one embodiment, the optical shutter is utilized in a security protection system based on detecting the change in absorption upon exposure of the optical shutter in the security protection system to high intensity radiation selected from the group consisting of ultraviolet radiation, visible radiation, and infrared radiation.
As will be appreciated by one of skill in the art, features of one aspect or embodiment of the invention are also applicable to other aspects or embodiments of the invention.